1. Field of the Invention
This invention relates to systems for indirectly measuring geometric dimensions related to openings in apertured exterior surfaces of parts such as ammunition cases based on direct measurements of the parts when fixtured at a measurement station.
2. Background Art
Traditional manual, gauging devices and techniques have been replaced to some extent by automatic inspection methods and systems. However, such automatic inspection methods and systems still have a number of shortcomings associated with them.
Inspection of defects on small arms ammunition cartridges and cases is a vital aspect in the manufacturing process, allowing for maintenance of a high level of quality and reliability in the munitions industry. Standards have been developed and applied by manufacturers for many years to assist in classifying various types of defects. Alternatively, a military standard is used such as that introduced in 1958 by the US Department of Defense, MIL-STD-636. For small arms ammunition calibers up to 0.50, this standard serves to evaluate and illustrate a practical majority of defects assembled as a result of extensive surveys covering all the small arms ammunition manufacturing facilities in the United States.
U.S. Pat. No. 4,923,066 discloses an automatic visual inspection system for small arms ammunition which sorts visual surface flaws at high speed according to established standards which can be tailored to fit specific needs. The system employs techniques for performing inspection independently of human inspectors and allows for quick changeovers in the type of ammunition to which it is applied. The system comprises interface apparatus for receiving a supply of ammunition cartridges and providing each cartridge with a predetermined orientation, conveying apparatus for locating each of the cartridges for inspection in at least one inspection station, apparatus for imaging selected areas of each cartridge to provide video surface feature data associated therewith, and apparatus for processing the video surface feature data to detect the presence of a predetermined set of characteristics and provide output signals in accordance therewith, the conveying apparatus being operated to sort each of the inspected cartridges in accordance with the output signals. A preferred embodiment comprises four subsystems, a feeding subsystem, an imaging and handling subsystem, an operation subsystem, and a computer subsystem. The imaging and handling subsystem provides each cartridge with the necessary orientation for inspection by a video camera feeding video surface feature data to an image processing computer. The image processing computer makes a very high speed computation based on image processing techniques to decide whether the cartridges have manufacturing defects for sorting purposes. Since many surface flaws look the same in two dimensions such as scratches and splits or acid holes and stains, special lighting of the cartridges is used so that discrimination between them can be achieved on the basis of off-specular reflections.
U.S. Pat. No. 7,403,872 discloses a method and system for inspecting manufactured parts such as cartridges and cartridge cases and sorting the inspected parts. The method and system inspect the manufactured parts for a wider variety of defects than previously possible. The system includes an illumination assembly for evenly illuminating a plurality of annular, exterior side surfaces of a part when the part is located in a circumference vision station with rings of strobed radiation to generate corresponding reflected radiation signals. A plurality of imaging detectors in the form of CCD cameras are located at the vision station to generate a plurality of side images. The system further includes at least one side image processor for processing the side images of each part to identify parts having an unacceptable defect. Mouth and primer vision stations are disclosed as well as the circumference vision station.
WO 2005/022076 discloses a plurality of light line generators (72) which generate associated beams of light (26) that intersect a part (14) to be inspected. Each beam of light (26) illuminates at least one side of the part (14) with a line of light occluded by the part (14), and at least three light responsive sensors (104) provide for generating a signal (24) responsive to an occlusion of a corresponding line of light on a corresponding side of at least one side of the part (14). Each of the light responsive sensors is responsive to an occlusion at a different azimuthal location. A processor (28) analyzes the signals (24) in relation to a measure of relative location of the part (14) from a motion (18) or position sensor. The part (14) may be released from a clamp (52) to drop through the beams of light (26), or the beams of light (26) may be moved relative to the part (14).
U.S. Pat. No. 6,313,948 discloses an optical beam shaper for production of a uniform sheet of light for use in a parts inspection system having a light source including a coherent light generator, a diffractive beam shaper, and lens elements.
U.S. Pat. No. 6,285,034 discloses an inspection system for evaluating rotationally asymmetric workpieces for conformance to configuration criteria. The system has a track for causing the workpieces to translate through a test section. The test section includes a plurality of electromagnetic energy sources. The plurality of electromagnetic energy sources are oriented with respect to the track such that the workpieces occlude the plurality of electromagnetic energy sources upon passing through the test section. The test section further has electromagnetic energy detectors for receiving the electromagnetic energy to provide output signals related to the intensity of the occluded electromagnetic energy incident on the electromagnetic energy detectors, and a signal processor for receiving and processing the output signals.
U.S. Pat. No. 6,252,661 discloses an inspection system for evaluating workpieces for conformance to configuration criteria. The system includes a track for causing workpieces to translate through a test section. The test section includes a light source for producing a uniform sheet of light. The light source is oriented with respect to the track such that the workpieces occlude the uniform sheet of light upon passing through the test section. The test section further has a video system for receiving the occluded uniform sheet of light, providing output signals related to the intensity of the occluded uniform sheet of light incident on the video system, and a signal processor for receiving and processing the output signals.
U.S. Pat. No. 6,959,108 discloses an inspection system wherein workpieces to be inspected are consecutively and automatically launched to pass unsupported through the field of view of a plurality of cameras. As a workpiece passes through the field of view of the cameras, a sensor is activated which communicates with a computer system to activate the cameras to capture an unobstructed image, or image data, of the workpiece. The image data is then analyzed by a computer program to verify whether the image data indicates that the workpiece does not meet established criteria and therefore is considered defective. If the image does not meet the established criteria, the workpiece is rejected and segregated from workpieces which have not been identified as defective.
U.S. Pat. No. 5,608,530 discloses a laser for producing a beam of radiation which is then refined in cross-sectional dimension by use of plano-cylindrical lenses. The refined beam of radiation falls incident on a part to be measured. The unobstructed portion of the beam is then bifurcated by a pair of reflective surfaces which produce non-parallel radiating beams. Each resulting beam comprises the unobstructed portion of radiation which has passed radially opposed halves of the part. The magnitude of radiation present in each non-parallel radiating beam is then measured.
U.S. Pat. No. 4,831,251 discloses an optical device for discriminating threaded workpiece by the handedness by their screw thread profiles. The device present a pair of light beams which pass generally tangent to the workpiece at angularly displaced positions. The light beams are inclined to follow the helix direction of a given handedness of a workpiece. Upon axial advancement of a workpiece through the device, a chopped output from the photodetectors indicates that the handedness of the threads matches the inclination of the light beams. The oppositely threaded workpiece, however, provides a generally constant DC output. With appropriate signal processing electronics, an automatic system for discriminating workpieces by thread handedness is provided.
U.S. Pat. No. 5,383,021 discloses a non-contact inspection system capable of evaluating spatial form parameters of a workpiece to provide inspection of parts in production. The system causes parts to be sequentially loaded onto an inclined track where they pass through a test section. The test section includes a length detection array for measuring the length of the workpiece, which includes a source generating a sheet of light oriented in the longitudinal direction of the workpiece. The profile of the parts are evaluated by one or more light sources also creating a sheet of light oriented transversed to the longitudinal axis of the parts. Single channel photodetectors are provided for each of the sources which provides an analog output of the extent to which each sheet of light is occluded by the part. These outputs are analyzed through appropriate signal processing hardware and software to generate length and profile data related to the workpiece geometry.
U.S. Pat. No. 5,568,263 discloses a non-contact inspection system capable of evaluating spatial form parameters of a workpiece to provide inspection of parts in production. The system causes parts to be sequentially loaded onto an incline track where they pass through a test section. The test section includes a length detection array for measuring the length of the workpiece, which includes a source generating a sheet of light oriented in the longitudinal direction of the workpiece. The profile of the parts are evaluated by one or more light sources also creating a sheet of light oriented transverse to the longitudinal axis of the parts. First and second pairs of single channel photodetectors are provided for each of the light sources which provides a pair of analog outputs of the extent to which each sheet of light is occluded by the part, as well as an ability to eliminate noise or scintillation caused by a point source of light, for example with a laser light source. These outputs are analyzed through appropriate signal processing hardware and software to generate length and profile data related to the workpiece geometry.
U.S. Pat. No. 4,852,983 discloses an optical system which simulates the optical effect of traveling over a large distance on light traveling between reference surfaces.
U.S. Patent Application Publication No. 2005/0174567 discloses a system to determine the presence of cracks in parts. The presence of cracks is determined through the use of an imaging device and illumination source. The part is moved along a track where it is sensed by a position sensor to initiate the inspection. The illumination source projects a sheet of light onto the part to be inspected. The line formed by the intersection of the sheet of light and the part is focused onto the imaging device. The imaging device creates a digital image which is analyzed to determine if cracks are present on the part.
U.S. Patent Application Publication No. 2006/0236792 discloses an inspection station for a workpiece including a conveyor, a mechanism for rotating the workpiece, and a probe. The conveyor includes a fixture for locating the workpiece and the conveyor is configured to translate the workpiece in a linear manner. A mechanism, such as a belt, engages the workpiece thereby rotating the workpiece within the fixture. The probe is configured to indicate if the workpiece conforms to quality criteria. To facilitate inspection while the conveyor translates the workpiece, the probe is attached to a stage where the stage is configured to move the probe synchronously with the workpiece over an inspection region.
U.S. Pat. No. 6,289,600 discloses a non-contact measuring device for determining the dimensions of a cylindrical object, such as a pipe. The device may use a programmable industrial robot with an arm terminating in a rotary joint, or wrist. A non-contact measurement assembly, which preferably includes a triangulation laser, mounted to the robot's wrist. The wrist includes a binary wrist encoder for providing the angular position of the wrist to an attached computer. Likewise, the laser provides a signal representative of the distance from the laser to the surface of the pipe to the computer. The robot positions the measurement assembly in a predetermined location within the pipe and rotates the measurement assembly. The computer correlates the measurements from the lasers with the angular position at which they were taken, and it analyzes this data to determine the dimensions of the pipe, including the true profile of the surface and cross-sectional shape.
U.S. Pat. No. 5,521,707 discloses a non-contact laser-based sensor guided by a precision mechanical system scans a thread form producing a set of digitized images of the thread form. The digitized images are analyzed to derive quantitative information about thread characteristics such as pitch, lead, root radius, flank angle, surface roughness, helix variation, and pitch diameter. Thread form data may be stored and later retrieved in order to provide traceability and verification of thread form measurements to a predetermined thread form specification. The apparatus and method of the invention can measure characteristics for shapes similar to threads, such as gears and dies used for cold forming processes. The thread measurement system can be mounted on thread making machines and used for on-line monitoring and control of the thread forming process.
U.S. Pat. No. 4,547,674 discloses a method and apparatus for inspecting gear geometry via optical triangulation. Preferred machine construction uses specialized geometrical relationships of sensor to gear, and specialized high accuracy photodetector array based laser triangulation sensor units of large range and high response speed.
U.S. Pat. No. 4,970,401 discloses a non-contact triangulation probe system including a base plate and a first non-contact triangulation probe including a light source mounted on a first movable slide. The first slide is disposed on the base plate and arranged for sliding motion therealong, a source of movement for the first slide being associated therewith. A first position sensor determines the relative position of the first probe and provides an output signal corresponding thereto. A second non-contact triangulation probe includes a light source mounted on a second movable slide. The second slide is disposed on the base plate and arranged for sliding motion in the same direction as the first slide, a source of movement for the second slide being associated therewith. A second position sensor determines the relative position of the second probe and provide an output signal corresponding thereto. The first and second probes are arranged to face each other such that the light beams emitted by the probes coincide on the same optical axis. A microcomputer is arranged to actuate the source of movement for the first and second slides, to receive the output signals from the first and second position sensors, and to receive output signals from the first and second probes.
U.S. Pat. Nos. 5,168,458 and 5,170,306 disclose methods and systems for gaging threaded fasteners to obtain trilobular parameters.
Other U.S. patents related to the invention include: U.S. Pat. Nos. 4,315,688; 4,598,998; 4,644,394; 4,852,983; 4,906,098; 5,521,707; 5,646,724; 5,291,272; 6,055,329; 4,983,043; 3,924,953; 5,164,995; 4,721,388; 4,969,746; and 5,012,117.
While the systems described in the above-noted commonly-owned U.S. patent applications provide an excellent tool for first article inspection, random sampling QA and for generating real-time process control feedback, there are several important features on parts such as ammunition cartridge cases (empty brass) which cannot be measured using the hardware configuration described in these systems. These features of interest include Mouth Inner Diameter, Mouth Wall Thickness, Primer Pocket Diameter and Primer Pocket Depth when the parts are cartridge cases.